This invention relates to ammonium nitrate and more particularly to methods of preventing the accidental detonation of ammonium nitrate.
It is well known that ammonium nitrate is a hazardous material to manufacture on an industrial scale, to handle commercially in large amounts, and to store in great masses in commercial warehouses and storage bins, especially for relatively long periods of time. As those skilled in the art have been aware, there have been unexplained accidents and explosions in the manufacture, handling, and storage of ammonium nitrate.
It was known that at temperatures ranging from about -18.degree. C. to the transition point occurring at 32.3.degree. C. the stable crystal form of ammonium nitrate is an orthorhombic bipyramidal form of specific gravity 1.715, designated by the Roman numeral IV. Between the transition point occurring at 32.3.degree. C. and the other transition point occurring at 84.degree. C. the stable crystal form is orthorhombic and of specific gravity 1.654, designated by the Roman numeral III. Lastly, between 84.degree. C. and 125.degree. C. the stable crystal form is tetragonal, designated by the Roman numeral II.
It was known in "Zur Sensibilitat von Ammoniumitratengegen Detonationsstoss," Chemiker Zeitung, Volume 96 (1972), pages 449-455 that the detonation sensitivity of ammonium nitrate to shock increases seriously after exposure to a few temperature cycles through the 32.3.degree. C. (90.degree. F.) transition point. Stabilizing agents like magnesium nitrate or boric acid/ammonium phosphate/ammonium sulfate, which have been added to ammonium nitrate to prevent cracking, caking, and reduction in the bulk density of the prills, also prevent increases in the sensitivity of the ammonium nitrate. These additives accomplish this by tying up the moisture which is necessary for the 32.3.degree. C. phase change from ammonium nitrate form III to form IV to occur. However, once such stabilizing agents become saturated, they can no longer function as phase stabilizing agents, "growth" and increased sensitivity then occur as with unstabilized ammonium nitrate. Thus, spraying with 0.5 percent water (an amount that the hygroscopic ammonium nitrate can readily take up from the atmosphere) followed by a few temperature cycles gave a product that detonated completely, even for the best stabilized ammonium nitrate.